Embryonic blood vessel development requires the differentiation of mesodermal cells into migratory endothelial cells that form tubular vessels, in nearby or distant tissues, in a reproducible manner. The molecular signals involved in this patterning process have not yet been fully defined. We hypothesize that the precursor cells are not intrinsically programmed but respond to exogenous signals for patterning cues, such as vascular endothelial growth (VEGF) secreted from the neural tube. Analyzing mesodermal tissue from mouse embryos in a three-dimensional collagen-gel culture-system will test this hypothesis. Specifically, the aims are to determine if murine paraxial mesoderm has vasculogenic potential in explant culture and to determine if VEGF is involved in the three dimensional patterning of blood vessels.